There are lots of videos on YouTube marked as inappropriate by users, and because of this YouTube restricts viewing of these videos to registered users only. If you do not have an account and want to view a flagged YouTube video you will get following message:

“This video may contain content that is inappropriate for some users, as flagged by YouTube’s user community. To view this video, please verify you are 18 or older by logging in or signing up.”

This is where NSFWYouTube can help, it is a simple web app that lets you view flagged YouTube videos without logging in or having a YouTube account. All you have to do is enter NSFW in front of “protected” YouTube video URL and hit enter.